Hypolimnetic oxygenation 2: oxygen dynamics in a large reservoir with submerged down-flow contact oxygenation (Speece cone)

Abstract

Horne AJ, Jung R, Lai H, Faisst B, Beutel, M. 2019. Hypolimnetic oxygenation 2: oxygen dynamics in a large reservoir with submerged down-flow contact oxygenation (Speece cone). Lake Reserv Manage. 35:323–337.

Low dissolved oxygen (DO) in the sediments of Camanche Reservoir, California (513 million m³, 31 km²), produced toxic hydrogen sulfide (H₂S). Direct hypolimnetic oxygenation suppressed H₂S without provoking early destratification and cold-water fish problems downstream. A cool, bubble-free plume directed horizontally over the sediments was chosen over a rising bubble plume. A submerged, down-flow contact oxygenator (Speece cone) pumped anoxic water from 5 m above the sediments to the top of a 7 m high cone to dissolve a counterflow of rising pure oxygen bubbles. The bubble-free, highly oxygenated discharge (80 mg/L) was diluted to fish-safe levels (8 mg/L) and directed up-reservoir via jets in a 45 m long manifold. Placing the cone on the bottom near the dam increased hydraulic pressure and doubled oxygen solubility. Poor-quality hypolimnion water (DO <2 mg/L, redox 18–100 mV, H₂S odors) was converted to good-quality water (DO 3–7 mg/L, redox >300 mV, no H₂S odors). Comparing preoxygenation hypolimnion DO decline (0.1 mg/L/d) with oxygenation temporarily switched off (0.23 mg/L/d) gave a full-scale estimate of induced hypolimnion oxygen demand. In 1994, the oxygenated plume moved 4.5 km upstream at 0.1 cm/s via natural water motion. No long pipes were needed. About 18% of the bottom hypolimnion was directly oxidized in the cone and 1.8 times the total volume was indirectly oxidized via entrainment in the plume. After 10 yr, oxygen additions were reduced by >50% with no deleterious effects.

Keywords:

• Deep water currents
• hypolimnion oxygenation
• sediment oxygen demand
• Speece cone

Acknowledgments

This paper is dedicated to the late Dr. Jim Sandusky, Lawrence Berkeley Laboratory, who developed the mathematical patchiness theory with me that was used to give the spatial data array used here (Fig. 7). Jim, a founder member of the Mo’ Waters band well known to NALMS conference attendees, was lost, along with nine others, when the ocean research vessel Holoholo sank off Hawaii in 1978. He was still in his early 30s. We thank the field crews of both Brown and Caldwell and EBMUD for a fine effort in continually providing good data at the many sites needed under sometimes difficult conditions. We also thank the three referees for their detailed and valuable assistance.